Processing aids in preparation of sbr flexible magnets



U.s. c1. 252-6254 United States Patent O 3,467,598 PROCESSING AIDS IN PREPARATION OF SBR FLEXIBLE MAGNETS William J. Kroenke, Brecksville, Ohio, assignor to The B. F. Goodrich Company, New York, N.Y., a corporation of New York No Drawing. Filed Jan. 16, 1967, Ser. No. 609,327 Int. Cl. H01f 1/117 4 Claims ABSTRACT OF THE DISCLOSURE Alkyl iminodiacetic acids and certain derivatives thereof assist in the combination of large volumes of fine barium ferrite particles with butadiene-styrene synthetic rubber polymers. The heavily loaded rubber stocks are then readily extruded into solid shapes for use as flexible magnets.

Background of the invention Solid metallic magnets are known. Solid ceramic magnets are known. For some uses, particularly where the magnets must be small and rounded or curved in shape, these solid magnets are not always useful. So-called flexible magnets have been developed which, in addition to this improvement, are less costly than rigid magnets. Flexible magnets consist of an elastomeric binder containing many particles of a magnetic compound. The binder has a degree of flexibility, allowing the magnet to be bent, curved or arced to fit a contour, and the magnetic particles or powder, dispersed throughout the binder, provide the magnetic strength desired. These bonded magnets are less hard and brittle than metal or ceramic magnets. They can be readily cut and shaped by punching, extruding, drilling and the like. Rubbery polymers are particularly favored as binder materials. Finely ground barium ferrite is particularly favored as a magnetic material. A problem that exists in making this type of magnet is that one needs a very high concentration of magnetic particles to obtain useful magnetic strength. The magnetically strongest magnet would consist solely of magnetic particles and would contain no binder at all, but such a material has no cohesive binding strength unless it is fired at very high temperatures, and it would then be a rigid structure. At the levels of magnetic powder loading, 60-65 volume percent, generally required for satisfactory magnetic strength, the binders cohesive strength is severely weakened. United States Patent 3,121,131 describes the making of magnets by milling 65% by volume barium ferrite into natural rubber. This mixture is useful in magnetic strength, but lacks physical strength to allow it to be extruded through a die to a desired shape. Crumbling occurs when the matrix rubber is loaded with magnetic filler to the extent that the matrix can no longer wet the filler particles to bind them. The patent teaches one to overcome this problem by milling the stock into thin sheets which are then plied to a desired thickness and laminated. The need to ply and laminate thin sheets to a desired thickness which can then be cut to a desired shape, leads to extra operations and higher costs. This invention provides a process for making SBR polymer binder containing a high volume percent barium ferrite that can be extruded through dies of any desired shape and then cut to any desired length.

Summary of the invention Among the rubbery polymers that one desires to use as binders for finely ground magnetic materials are the butadiene-styrene synthetic rubbers known as SBR. The SBR polymers are competitive in cost and most properties with natural rubber and can serve equally Well as a matrix for 3,467,598 Patented Sept. 16, 1969 magnetic particles. These polymers contain from 22% to 45% bound styrene by weight. To achieve sufliciently high magnetic strength, 60-65 volume percent barium ferrite must be combined with the SBR binders. While this amount of barium ferrite can be milled into natural rubber, as shown in Patent 3,121,131, this natural rubberferrite mixture does not have strength to enable one to extrude it in thick shapes of A or more thickness. If SBR is substituted for natural rubber in the formation of the rubber-ferrite mix, it is found that only about 50 volume percent barium ferrite can be added before the mixture loses cohesive strength and becomes brittle and crumbles. In addition, the material has a low maximum energy product of about 100,000 gauss-oersteds whereas a value of at least 700,000 gauss-oersteds is required for a useful product. Higher amounts of ferrite cause the stocks to crumble and fall from the mills. These stocks cannot even be sheeted in thin slabs as the prior art patent teaches with the natural rubber-ferrite mixtures. The use of processing aids with rubber stocks is known. Processing aids are not universal in nature, however. A processing aid for natural rubber will not necessarily improve the processing of a given synthetic rubber. This invention provides processing aids which enable one to mill 6065 volume percent barium ferrite into SBR polymers to provide compositions which can be extruded into desired shapes for use as mag netic materials.

The processing aids discovered for this use are soluble in or compatible with conjugated diolefin rubbers. They comprise materials having the structure wherein R is a hydrocarbon group having from 6 to 20 carbon atoms, R is selected from the group consisting of hydrogen and C-H CO0H, R" is a saturated hydrocarbon group having from 2 to 10 carbon atoms, x is a number of from 0 to 1, and y is a number of from 1 to 2. When x is 0, y is 1, and when x is 1, y is 2.

Illustrative specific compounds falling into this class are the following:

CrsHar-NCH2CH2CHzCHsCHzCHz-N(CH2C O OH):

These materials are generically described as alkyl iminopolyacetic acids.

These processing aids may be incorporated into the rubber polymer which is to be used as the binder component for a magnet stock in any conventional manner such as by mill-mixing or mixing in an internal mixer such as the Banbury.

In the practice of this invention it is desirable to use from about 4 to about 10 parts by weight of processing aid per 100 parts by weight of rubber polymer.

The preferred magnetic powder for use in mixing these flexible magnet stocks is barium ferrite. The particle size is preferably ultrafine, from about 0.5 micron to about 5 microns in diameter. The general formula is BaFe O Strontium ferrite or other ferromagnetic powders may also be used.

The magnetic properties of the SBR flexible magnets are determined on extruded strips about 0.13 in. thick and 0.38 in.'wide. The strips are magnetized to saturation with a coil magnetizer that is designed to provide a concentration of strong alternating north and south poles along one of the faces of the strip; opposing weak south and north poles exist on the opposite parallel face. The maximum pull strengths in pounds attained across a 0.015- inch air gap are determined for both the magnetically strong and weak sides of the magnetized strips. The strips are one foot long, so that the strengths are in pounds per foot. Because of the geometry of the pole arrangement, the maximum pull strength measured for the strong side is a measure of its ability to serve in a latch-magnet application; the stronger the pull strength, the stronger the strength of the magnet in a latch-type application.

The maximum energy product, (BH) max., which corresponds to the point on the demagnetization portion of the hysteresis loop which will give the maximum energy output per unit volume of magnetic material external to the magnet, is determined with a standard magnetic permeamrneter. This property is an important design factor in specifying permanent magnets in electrical applications such as to provide field excitation in DC. and AC. 1110- tors and generators.

Description of the preferred embodiments The present invention will be further illustrated by the following examples wherein the amounts of the various ingredients are expressed in parts by Weights unless otherwise indicated.

Preparation of processing aids Dodecyliminodiacetic acid is prepared as follows: chloracetic acid (1.1 mole) in 800 ml. of ethanol is neutralized by the addition of 125 ml. of N aqueous sodium hydroxide. Dodecyl amine (0.5 mole) is added to the mixture and the solution is heated to 80 C. The pH is maintained at from 8 to 10 by the gradual addition of more 10 N sodium hydroxide solution until the theoretically required amount of sodium hydroxide has been added. The reaction mixture is then brought to room temperature and the dodecyliminodiacetic acid is precipitated by bringing the pH of the mixture to 2 with concentrated hydrochloric acid. The product is isolated by filtration and is washed twice With distilled Water and dried to a constant weight of 141.3 g. (94% of theory) and is designated processing aid (A).

A processing aid having the structure wherein R is a mixture of alkyl groups having an average of 18 carbon atoms is prepared as follows: chloroacetic acid (2.24 moles) in 400 ml. of methanol is neutralized with 31% NaOH solution. Duomeen T wherein R is a mixture of alkyl groups having an average of 18 carbon atoms (0.25 mole), is added. The reaction mixture is brought to 70-73 C. and the pH of the reaction mixture is maintained at 8-10 by the addition of more 31% NaOH solution until the pH becomes fairly constant for a period of time. The mixture is cooled and the product is precipitated with hydrochloric acid (pH of 2). The solid is isolated by filtration, washed and dried and is designated processing aid (B).

Example A charge of 65.7 grams of a commercial butadienestyrene copolymer, Ameripol 1013, containing 43% bound styrene is set up rolling on a rubber mill at about 100 F. Next 7.4 grams of dodecyliminodiacetic acid, processing aid (A), are added to the rubber and milled in over a period of about 2 minutes. Finally, 741.0 g. of ultrafine barium ferrite are added and milled into the rubber, processing aid mixture. Total milling time is about ten minutes. The fiexible sheet stock is easily extruded into a smooth, flexible strip through a one inch die forming a strip .38" Wide and .13 thick at 170-240 F. This operation is designated Run A. Runs B and C follow the same procedure and use the same materials, but the amounts of barium ferrite are varied to give a range of volume percent loadings of the SBR binder with magnetic powder. Data are set forth in Table 1. The control is a standard commercial flexible magnet based on barium ferrite loaded chlorosulfonated polyethylenebutene rubbery copolymer binder.

TABLE 1 Volume, Max. Pull (BH) max.,

percent Strength gauss- Tensile, Run BHFBBOID (lb/ft.) oersteds p.s.i

At the same level of loading the magnets made according to this invention have a much higher energy product and approximately the same strong side pull strength as the control.

Experimental magnets A and B are compared to the control in a stiffness test on the Tinius-Olsen tester. Data are set forth in Table 2.

TABLE 2 5 load (g.) 10 load (g.) g. Load Angle 48 87 12. 13 20 20 at 30 g. 21 31 20 at; 43 g.

The magnets of the invention are too compliant to permit a reading to be obtained at a load of 100 g., that is, they are much more flexible than the control.

When Ameripol 1506, a butadiene-styrene copolymer analyzing 22.5% bound styrene is substituted in the above procedure for Ameripol 1013, data are obtained as shown in Table 3.

TABLE 3 Volume, Max. Pull (BH) max.,

percent Strength gauss- Tensile, Run BaFeizOm (lb/ft.) oeisteds p.s.i.

When processing aid (B) is substituted for processing aid (A) in the procedure shown above, with the Ameripol 1013 binder, a series of flexible magnets is obtained with properties essentially the same 'as those set forth in Table 1.

I claim:

1. Magnetic composition comprising 100 parts by weight butadiene-styrene rubber copolymer as binder, at least 60 volume percent barium ferrite as magnetic powder, and as processing aid, from 4m 10 parts of a material having the formula where R is a hydrocarbon group having from 6 to 20 carbon atoms, R is selected from the group consisting of hydrogen and CH COOH, R" is a saturated hydrocarbon group having from 2 to 10 carbon atoms, x is a number from 0 to 1, and y is a number from 1 to 2 and when x is 0, y is 1 and when x is 1, y is 2.

2. The magnetic structure of claim 1 wherein said processing aid comprises dodecyliminodiacetic acid.

3. The method of making a flexible magnetic structure comprising mixing together butadiene-styrene rubber copolymer as a binder, barium ferrite as a magnetic powder and as a processing aid a material having the formula where R is a hydrocarbon group having from 6 to 20 carbon atoms, R is selected from the group consisting of hydrogen and CH COOH, R" is a saturated hydrocarbon group having from 2 to 10 carbon atoms, x is a number from 0 to 1, and y is a number from 1 to 2 and when x is 0, y is 1 and when x is 1, y is 2, extruding said mixture through a die to form a shaped strip and cutting said shaped strip to a desired length.

4. A method of claim 3 wherein the said processing aid comprises dodecyliminodi'acetic acid.

References Cited UNITED STATES PATENTS MORRIS LIEBMAN, Primary Examiner SAMUEL L. FOX, Assistant Examiner US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,467,598 September 16, 1969 William J. Kroenke It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 46, "C O should read C H Signed and sealed this 24th day of February 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Edward M. Fletcher, 11'.

Commissioner of Patents Attesting Officer 

